[31.03] New 3-D magnetic model for prominences based on dipped \\field lines and compared with observations

G. Aulanier (NRL), P. Demoulin (DASOP, Observatoire de Meudon)

Despite of the large number of 2D and 3D models for the
magnetic fields in prominences, none has been succesfully
directly compared with observational data untill recently,
even if many of them still satisfied some well established
observational results. This has led to a never ending
controversy between theorists and observers, about the
relevance of dipped field lines for mass support against
gravity in these objects.

Here we present a new 3D magnetohydrostatic model based on
dipped field lines. The main body of the filament is formed
by a twisted flux rope in a bipolar region, and we show how
small parasitic polarities near the neutral line lead to a
local perturbation of the magnetic fields in the corona,
leading to the formation of lateral dips, which appear aside
from the flux rope. We show that these are formed by local
expansions of the fluxe rope, as well as by the bending of
some surrounding sheared field lines, toward the
photospheric parasitic polarities. We suggest that these
lateral dips can form lateral feet of filaments. Moreover
the global magnetic configuration shows in a natural fashion
a very large number of typical observational aspects of
prominences.

Using a magnetogram obtained by SOHO/MDI on 09/25/96 as
boundary conditions, we extrapolate the magnetic field under
the assumptions of the model. Comparing the 3D distribution
of dips with the morphology of the filament observed in
H\alpha on the German VTT (Tenerife) at the same time, we
show a good correlation between the dips and the filament
body, as well as with its lateral feet.

All these results suggest that the model is well adapted for
the description of the magnetic field in filaments and their
close environement. Furthermore its direct comparison with
observations provide evidence in favor of dipped field lines
in prominences.

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